Attention is highly critical tp our conscious experience. A failure to focus or to shift attention can be devastating, and may contribute to neurological and psychiatric diseases such as attention deficit hyperactivity disorder (ADHD), dyslexia, and schizophrenia. Experiments from the Desimone lab and others have shown that attention alters neural activity in many visual areas and synchronizes activity across brain regions. There is increasing evidence for the presence of top-down modulatory mechanisms mediating attention. However, the precise neural circuitry underlying these effects is largely unl<nown, and it remains difficult to establish causal linl<s between activities in specific neural circuits or cell types, and emergent behaviors and pathologies. Accordingly, I will develop the use ofthe technologies for activating and silencing specific types of neurons with millisecond-timescale precision, with which to perform a timeresolved analysis of necessity and sufficiency of specific prefrontal neural activity patterns in mediating topdown control of attention.